1. Field of the Invention
This invention relates to portable, battery-powered communication devices such as cellular telephones and pagers. More particularly, it relates to a portable communication device incorporating both a cellular telephone and a pager. It also relates to methods and devices for extending battery life during operation of such devices.
2. Description of Related Art
During the past two decades, rapid proliferation of portable communication devices has been nothing short of amazing. During the past 15 years, cellular telephones have progressed from being a novelty to a ubiquitous appliance. The use of pager devices has also become widespread.
The following equipment examples are illustrative of the current state of this burgeoning industry. In the latter half of 1996, Nokia, a manufacturer of communications equipment, announced the introduction of the Nokia 9000 Communicator, a portable communication system that combines digital, voice and data services, as well as personal organizer functions in a single, compact unit. The Nokia device incorporates processing capability provided by an Intel 24 MHz 386 microprocessor, flash memory, and a powerful, memory-efficient graphical user interface (GUI) operating system named GEOS developed by Geoworks, Inc. The Nokia communication system is designed to work in combination with a hand-held computer screen produced by Reflection Technology, Inc., a manufacturer of virtual display technology and wireless messaging equipment. The computer screen, which displays a full 12-inch page of graphics and text, connects with cellular or land line phones to allow a mobile user to receive, read, store and send faxes without the use of a laptop computer. The device features a virtual keyboard with which the user may create memos and respond to faxes, and a full-screen menu that allows users to choose certain functions, such as view, send, enlarge and reduce. The device can store approximately 25 pages and has a built-in directory that stores more than 100 names and fax numbers for use with the unit's auto-dial feature.
In the case of a portable combination electronic device, one of the constituent devices typically consumes more power than the other during operation. A combination portable communication device incorporating both a cellular telephone and a pager is one such combination device. Power consumption of the cellular phone, particularly in the transceive mode, is typically several orders of magnitude greater than that of a pager device. For example, a typical cellular telephone with a 400 mAh nickel-cadmium battery will operate in the transmit-receive mode for only about 70 minutes before the battery must be charged or replaced. Standby time for the same battery is about 17 hours. Most of the power consumed during standby mode is required to operate the periodic query function which maintains cellular phone orientation with respect to the cellular grid. Pagers, on the other hand, require far less power to operate because they are, in the most basic mode of operation, merely radio receivers. Thus, they are generally endowed with much greater battery life. A standard beeper powered by a single AA-size alkaline power cell will operate continuously for four to six weeks if only the beeper notification mode is employed. Operating the same pager in the vibrator notification mode can halve battery life.
When a pager device and a cellular phone are combined into a single unit having a single battery power supply, maximum useful operating life of the pager between battery charges is largely dictated by battery life of the cellular telephone operating in standby mode. When the transmit-receive mode is employed, operating life of the pager on a single charge can be cut dramatically. This is particularly true where the user has little control over the number of incoming calls. Thus, even though the pager function may be more critical to the user, the pager function may be rendered useless by incoming telephone calls which drain the battery to the point where both the pager function and the telephone function are inoperative due to battery discharge below the critical operating voltage.
FIG. 1 depicts a circuit which has heretofore been utilized to control one of two or more electronic devices powered by a single depletable power supply where the device to be controlled requires a clock signal input for operation. A precision reference voltage VR is supplied to the inverting terminal (i.e., the "-" terminal) of comparator 102, and a sample voltage VS (taken from a voltage divider 101 constructed from resistors R1 and R2) is supplied to the non-inverting terminal (i.e., the "+" terminal) of comparator 102. The values of resistors R1 and R2 are selected so that the sample voltage VS is greater than VR, with the difference between VS and VR corresponding to the voltage range selected for continuous operation of an electronic device. The intermediate output VO1 from comparator 102 is fed to one of a pair of inputs to NAND gate 103. A clock signal CLK is fed to the other input. As long as VS is greater than VR, the current path through resistor R3 will maintain VO1 high, and an inverted clock signal CLK* will be passed through NAND gate 103. When VS drops below VR, comparator 102 will pull VO1 low. The signal CLK* is utilized to operate a second device. In order to prevent oscillations about the set turnoff point, hysteresis is provided at the output via a feedback path 104 through resistor R4.